Vacuum Heat Insulating Material, Method of Producing Vacuum Heat Insulating Material, and Heat Insulating Box Body Using Vacuum Heat Insulating Material

ABSTRACT

Disclosed is a vacuum heat insulating material. Also disclosed is a heat insulating box using the vacuum heat insulating material. The vacuum heat insulating material includes a core member and envelope members having gas-barrier properties and including heat-seal layers. The envelope members are opposed to each other in such a manner that the core member is disposed between the heat-seal layers. The envelope members are entirely heated to a temperature at which the heat-seal layers are melted, and the heat-seal layers are heat sealed to each other by applying uniform pressure to the entire envelope members from outside to inside the envelope members.

This application is a U.S. National Phase Application of PCTInternational Application PCT/JP2005/022339.

TECHNICAL FIELD

The present invention relates to a vacuum heat insulating material, amethod of producing the vacuum heat insulating material, and a heatinsulating box such as a refrigerator, which uses the vacuum heatinsulating material.

BACKGROUND ART

With increasing concern over the protection of global environment inrecent years, energy saving in household electrical appliances hasbecome an urgent issue. One proposed solution to this problem is to usevacuum heat insulating materials in order to eliminate unnecessary heattransfer.

A vacuum heat insulating material is formed of a core member andenvelope members which cover the core member. The core member is made offoamed resin, fibrous material, or the like. The vacuum heat insulatingmaterial is vacuum-sealed to lower thermal conductivity of gas. Theinsulation performance can be maintained only by maintaining the vacuumheat insulating material in a vacuum environment. During a long periodof operation, however, gases such as air and water vapor may enter intothe vacuum heat insulating material through resin layers, which are heatsealed to each other at the edges of the envelope members. Thisgradually deteriorates the degree of vacuum and hence the insulationperformance.

Japanese Patent Unexamined Publication No. 2000-104889 shows a method ofproducing a vacuum heat insulating material that prevents thedeterioration of the vacuum due to the entry of gas or water fromoutside.

FIG. 9 shows a sectional view of the conventional vacuum heat insulatingmaterial. FIG. 10 shows a sectional view of an envelope member of theconventional vacuum heat insulating material. As shown in FIGS. 9 and10, vacuum heat insulating material 1 is formed of core member 2 and abag-like envelope consisting of top envelope member 3 a and bottomenvelope member 3 b larger than top envelope member 3 a and protrudingat an edge. The bag-like envelope is sealed at edge-seal portion 4 andfolded portion 5 thereof by using an adhesive layer so as to bemaintained in a vacuum. In folded portion 5, one end of bottom wrapper 3b that is protruded from top wrapper 3 a is folded back so as to havetwo stacked sealing layers.

Each of top and bottom envelope members 3 a and 3 b is formed of topheat seal layer 7 and bottom heat seal layer 8 with aluminum foil layer6 disposed therebetween. Aluminum foil layer 6 has gas-barrierproperties. Top heat seal layer 7 and bottom heat seal layer 8 are madeof high-density polyethylene. Bottom heat seal layer 8 and top heat seallayer 7 of top envelope member 3 a are sandwiched between two bottomenvelope members 3 b so as to form folded portion 5. Folded portion 5 isheat sealed to form inner sealing layer 9 and outer sealing layer 10.

The inner sealing layer is prevented from being exposed outside so as tosuppress the deterioration of the vacuum of the envelope. As a result,the vacuum heat insulating material can maintain the insulationperformance.

Japanese Patent Unexamined Publication No. 2004-197935 shows a method ofproducing a vacuum heat insulating material as follows: A planar coremember is disposed between the respective heat-seal layers of twoopposed envelope members having gas-barrier properties. Then, theenvelope members, including a portion having the core member disposedtherebetween, are pressed under reduced pressure between hot plates madeof an elastic body so that the opposed heat-seal layers are heat sealedalong the shape of the core member. This method allows the heat-seallayers to have a larger width in the peripheries of the core member.This suppresses the deterioration of the vacuum in the envelope members,thereby maintaining the insulation performance of the vacuum heatinsulating material.

It is, however, difficult from a manufacturing standpoint to heat sealfolded portion 5 in such a manner as to have two sealing layers: innersealing layer 9 and outer sealing layer 10 as in the above conventionalstructure. This may cause wrinkles or sealing defects.

As another problem, top and bottom heat seal layers 7 and 8, which aresealed between inner and outer sealing layers 9 and 10, are required tobe made of a material suitable for heat sealing, thereby narrowing therange of materials suitable for surface protection. For example,high-density polyethylene is suitable for heat sealing, but is not forsurface protection due to its low strength properties, especiallyscratch resistance and pierce resistance. As a result, the vacuum heatinsulating material may have pinholes when handled inappropriately afterits manufacture.

On the other hand, in the method shown in Japanese Patent UnexaminedPublication No. 2004-197935, the envelope members, including the portionhaving the core member disposed therebetween, are heat sealed by beingpressed between the hot plates made of an elastic body. The pressure ofthe hot plates can be effectively applied to the portion of the envelopemembers that has the core member disposed therebetween, but not to theportions of the envelope members that do not have the core membertherebetween. Therefore, the core member needs to be compressible to athickness of not more than several millimeters. Using a core memberhaving a comparative large thickness may cause the portions of theenvelope members that do not have the core member therebetween to bepressed insufficiently, thereby causing defective heat sealing.

If the load of the hot plates is increased in order to apply sufficientpressure to the portions of the envelope members that do not have thecore member therebetween, the core member may be compressed too much. Asa result, the core member becomes to have a larger solid thermalconductivity, thereby degrading the insulation performance of the vacuumheat insulating material. Moreover, it is difficult to control thepressure applied to the portions of the envelope members that do nothave the core member therebetween, that is, the portions where theenvelope members are to be heat sealed to each other. This is becausethe pressure tends to depend on the flexibility and elasticity of thehot plates and the shape and thickness of the core member.

SUMMARY OF THE INVENTION

The present invention provides a vacuum heat insulating material whichis unsusceptible to wrinkles, sealing defects, pinholes, and othersimilar problems, and has high resistance to scratch and pierce. Theinvention also provides a heat insulating box such as a refrigeratorusing this vacuum heat insulating material in order to achieveenergy-saving.

The vacuum heat insulating material of the present invention includes acore member and envelope members having gas-barrier properties and eachincluding a heat-seal layer, the envelope members are opposed to eachother in such a manner that the core member is disposed between theheat-seal layers. The entire envelope members are heated to atemperature at which the heat-seal layers are melted; and the heat-seallayers are heat sealed to each other by applying uniform pressure fromoutside to inside the envelope members at least to a first portion ofthe envelope members that faces the core member, and a second portion ofthe envelope members that is in a vicinity of the core member.

In this structure, even if the core member has a comparative largethickness, the seal width to be heat sealed is extended as far as theedges of the core member. This makes it unnecessary to fold back theheat-seal layers when the envelope members are sealed by heat sealing.Consequently, the heat sealing can be performed as simply as theconventional well-known heat sealing without causing wrinkles or sealingdefects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a vacuum heat insulating materialaccording to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of an essential part of the vacuumheat insulating material according to the first embodiment of thepresent invention, showing a peripheral potion of the vacuum heatinsulating material.

FIG. 3 shows a schematic sectional view of a production device forproducing the vacuum heat insulating material according to the firstembodiment of the present invention.

FIG. 4 shows a sectional view of a vacuum heat insulating materialaccording to a second embodiment of the present invention.

FIG. 5 shows a schematic sectional view of a production device forproducing the vacuum heat insulating material according to the secondembodiment of the present invention.

FIG. 6 shows a sectional view of a vacuum heat insulating materialaccording to a third embodiment of the present invention.

FIG. 7 shows a schematic sectional view of a production device forproducing a vacuum heat insulating material according to a fourthembodiment of the present invention.

FIG. 8 shows a schematic sectional view of a refrigerator, which is aheat insulating box according to a fifth embodiment of the presentinvention.

FIG. 9 shows a sectional view of a conventional vacuum heat insulatingmaterial.

FIG. 10 is an enlarged sectional view of an envelope member as acomponent of the conventional vacuum heat insulating material.

REFERENCE MARKS IN THE DRAWINGS

-   11, 19, 22 vacuum heat insulating material-   12, 12 a, 12 b, 23 envelope member-   13, 24 core member-   14, 14 a, 14 b heat-seal layer-   26 sealing portion-   27 secured sealing portion-   28 first protective layer-   30 gas barrier layer-   32 reduced pressure space-   35 refrigerator (heat insulating box)-   36 outer box-   37 inner box-   38 foam insulation material-   51, 55 first portion-   52, 56 second portion-   53, 57 third portion

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The vacuum heat insulating material of the present invention includes acore member and envelope members having gas-barrier properties. Theenvelope members each include a heat-seal layer and are opposed to eachother in such a manner that the core member is disposed between theheat-seal layers. The heat-seal layers are heat sealed to each other byheating the entire envelope members to a temperature at which theheat-seal layers are melted and by applying uniform pressure fromoutside to inside the envelope members throughout a first portion of theenvelope members that at least faces the core member and a secondportion of the envelope members that is in a vicinity of the coremember.

As described above, the opposed heat-seal layers are heat sealed to eachother by entirely heating the envelope members to the temperature atwhich the heat-seal layers are melted and by applying the uniformpressure from outside to inside the envelope members throughout thefirst portion and the second portions of the envelope members.Consequently, even when the core member has a comparatively largethickness such as larger than 10 millimeters, the predetermined pressurecan be applied to the portions of the envelope members that do not havethe core member therebetween, without compressing the core member toomuch. The aforementioned portions are the portions where the heat-seallayers are to be heat sealed to each other. This ensures the heatsealing.

Consequently, even when the core member has a comparative largethickness, the vacuum heat insulating material is prevented fromsuffering wrinkles in the vicinity of the core member, so that the wholeportions where the envelope members are in contact with each other underthe atmospheric pressure can be securely heat sealed. The heat sealedportion can extend the region as far as the edges of the core member soas to improve sealing performance. The heat sealed portions where theopposed heat-seal layers are heat sealed to each other can havehomogeneous quality and reliability. As a result, the vacuum heatinsulating material having long-term reliability can be provided.

In the vacuum heat insulating material of the present invention, thecore member may be sealed under reduced pressure between the envelopemembers. The opposed heat-seal layers are heat sealed to each other byheating the entire envelope members to the temperature at which theheat-seal layers are melted and by applying the uniform pressure fromoutside to inside the envelope members to the entire envelope members.Consequently, even when the core member has a comparatively largethickness exceeding 10 millimeters, the predetermined pressure can beapplied to the portions of the envelope members that do not have thecore member therebetween, without compressing the core member too much.The aforementioned portions means the portions where the envelopemembers are to be heat sealed to each other. This ensures the heatsealing.

Consequently, even when the core member has a comparative largethickness, the vacuum heat insulating material is prevented fromproducing wrinkles in the vicinity of the core member, so that theportions where the envelope members are in contact with each other underthe atmospheric pressure can be securely heat sealed. The heat sealedportion can extend the region as far as the edges of the core member soas to improve sealing performance. The heat sealed portion where theopposed heat-seal layers are heat sealed to each other can havehomogeneous quality and reliability. As a result, the vacuum heatinsulating material having long-term reliability can be provided.

The vacuum heat insulating material of the present invention may haveinside the envelope members reduced in pressure in order to previouslyheat seal third portions thereof which are outside the second portionsthereof. This allows the heat sealing to be performed as simply as thenormal well-known heat sealing without suffering wrinkles or sealingdefects. Furthermore, the heat-sealing can be applied to the portionswhere the envelope members used to be merely in contact with each otherand not sealed to each other. This extends the region to be heat sealedso as to improve sealing performance. As a result, the vacuum heatinsulating material having long-term reliability can be provided.

In the vacuum heat insulating material of the present invention, thepressure may be applied by a fluid. Using a fluid facilitates theapplication of the uniform pressure to the entire envelope members. Thepressure may be applied by the fluid directly to the envelope members.This prevents the envelope members from being stressed or scratched,making the vacuum heat insulating material with less pinholes and othersimilar problems.

In the vacuum heat insulating material of the present invention, thefluid may be a gas. A gas is easier to handle and has less adverseeffects on the envelope members than a liquid, which requiresafter-treatment such as removal of the liquid from the envelope memberswhen adhered thereto. Furthermore, the pressure can be atmosphericpressure. The atmospheric pressure can be uniformly applied from outsideto inside the envelope members to the entire envelope members only bycovering the core member with the envelope members in a space reduced inpressure substantially to vacuum and then returning the reduced inpressure space to normal pressure. The atmospheric pressure is highenough to apply at the heat sealing the envelope members, so that thereis no need to provide a pressuring device. This simplifies the provisionof the vacuum heat insulating material.

In the vacuum heat insulating material of the present invention, theheat-seal layers may be polyethylene. Since polyethylene can be sealedat comparatively low temperatures, it becomes easier to perform the heatsealing by additional heating. As a result, the vacuum heat insulatingmaterial can be provided at low cost. Furthermore, the envelope membermay have a protective layer of polyethylene terephthalate as theoutermost layer. Providing the envelope members with the outermostlayers made of a material suitable for surface protection can make theenvelope members more resistant to scratch and pierce and prevents anoccurrence of pinholes and other similar problems. As a result, thevacuum heat insulating material having long-term reliability can beprovided. Polyethylene terephthalate is inexpensive, so that the vacuumheat insulating material of the present invention can be provided at lowcost.

A method of producing a vacuum heat insulating material according to thepresent invention is performed as follows: The core member is coveredwith envelope members having a gas barrier layers and a heat-seallayers. Inside of the envelope members are reduced in pressure, theperipheries of the envelope members are heat sealed, and non-sealedportions inside the peripheries are heat sealed by uniformly applyingheat to melt the heat-seal layers. The non-sealed portions mean theportions where the envelope members are merely in contact with eachother and not sealed to each other. This method allows to heat seal thenon-sealed portions of the envelope members that cannot be heat sealedby the ordinary method. In the vacuum heat insulating material thusproduced, the portions of the heat-seal layers that are in contact witheach other are entirely heat sealed to each other.

In the method of producing a vacuum heat insulating material of thepresent invention, the heat may be applied out of contact with theenvelope members. This allows the envelope members to be heated withoutthe hot plates or the like that fit the shape of the core member. Inaddition, the envelope members have no stress according to creases orscratches and an occurrence of pinholes and other similar problems canbe prevented. Alternatively, the heat may be applied by radiant heatfrom a heater. This allows the envelope members to be heated out ofcontact with the heater and also in a reduced pressure space.

Another method of producing a vacuum heat insulating material accordingto the present invention is as follows: The core member is covered withenvelope members having gas barrier layers and a heat-seal layers in areduced pressure space. The heat-seal layers are brought to apredetermined molten state while the reduced pressure space ismaintained at a temperature higher than the melting point of theheat-seal layers. The reduced pressure space is then returned to normalpressure, while pressing the peripheries of the envelope members, andthe envelope members including the non-pressed portions can be heatsealed to each other. This method allows the envelope members to benormally heat sealed by heat pressing and to be heat sealed by using theatmospheric pressure at the same time, so that it takes less time toproduce the vacuum heat insulating material.

The heat insulating box of the present invention includes an outer box,an inner box, a foam insulation material filled in a space formed by theouter box and the inner box, and a vacuum heat insulating materialprovided between the outer box and the inner box. The vacuum heatinsulating material is at least partly buried in the foam insulationmaterial. The vacuum heat insulating material is one of theaforementioned vacuum heat insulating materials or produced by one ofthe aforementioned methods of producing a vacuum heat insulatingmaterial. The heat insulating box can maintain heat insulatingperformance for a long time because of the vacuum heat insulatingmaterial having long-term reliability. The heat insulating box can beapplied, for example, to a refrigerator to allow it to maintain energysaving performance for a long time.

Embodiments of the present invention will be described as follows withreference to drawings. Note that the present invention is not limited tothese embodiments.

First Embodiment

FIG. 1 shows a sectional view of a vacuum heat insulating materialaccording to a first embodiment of the present invention. FIG. 2 is anenlarged sectional view of an essential part of the vacuum heatinsulating material according to the present embodiment. FIG. 3 is aschematic sectional view of a production device for producing the vacuumheat insulating material according to the present embodiment. In FIG. 1,vacuum heat insulating material 11 has core member 13 and two envelopemembers 12 which cover core member 13 and inside of the envelope members12 is vacuum-sealed. Envelope members 12 have first portion 51 whichfaces the core member and second portions 52 which are in the vicinityof the core member. First portion 51 and second portions 52 are unitaryformed.

Envelope member 12 includes heat-seal layer 14. The two heat-seal layer14 of upper and bottom envelope members 12 are heat sealed along coremember 13 and integrally heat sealed to each other as far as the edgesof core member 13. Thickness of heat-seal layers 14 have is maintainedconstant. Core member 13 is a glass wool board having a density of 275kg/m³ dried for one hour at 140° C. in a drying furnace. Core member 13may be a planar porous body having a gas phase ratio of about 90%. Theporous body may be made of any well known industrially usable materialin the form of powder, foam, fiber, or the like, depending on theapplication or required characteristics.

In FIG. 2, envelope member 12 is made of a laminate film consisting offirst protective layer 28, second protective layer 29, gas barrier layer30, and heat-seal layer 14 in this order from outside to inside. Thesetwo laminate films are opposite to each other. First protective layers28 are made of polyethylene terephthalate film, and second protectivelayers 29 are made of nylon film. Gas barrier layers 30 are made ofaluminum foil, and heat-seal layers 14 are made of very low densitypolyethylene (VLDPE) film, which is a kind of polyethylene. Thepolyethylene terephthalate film is 12 μm thick, the nylon film is 15 μmthick, the aluminum foil is 6 μm thick, and the very low densitypolyethylene (VLDPE) film is 50 μm thick.

Envelope members 12 are preferably about 0.1 mm thick to preventwrinkles and sealing defects and to improve sealing quality. Envelopemembers 12 are preferably made of plastic laminate film havinggas-barrier properties. Envelope members 12 can also preferably beelongated and bent depending on the shape or size of core member 13during the production of vacuum heat insulating material 11 as far asthe gas-barrier properties are not affected.

Vacuum heat insulating material 11 is produced by using productiondevice 15 shown in FIG. 3. Production device 15 has two hot plates 17 attop and bottom in chamber 16 and is connected to pipes 18 a and 18 b attop and bottom of chamber 16. Pipes 18 a and 18 b are used to create thevacuum so as to increase the degree of vacuum, and to release the vacuumso as to decrease the degree of vacuum.

Envelope members 12 a and 12 b and core member 13 are placed inproduction device 15. Chamber 16 is divided into two spaces 16 a and 16b by envelope members 12 a. Envelope members 12 are heated by top andbottom hot plates 17 to the melting point of heat-seal layers 14, andentire chamber 16 is evacuated through pipes 18 a and 18 b. When chamber16 reaches a predetermined degree of vacuum, pipe 18 a releases thevacuum only in chamber 16 a first, and then releases the vacuum inchamber 16 b so as to introduce the atmosphere. Such a control ofatmospheric introduction improves sealing quality.

Hot plates 17 only need to be heated to make heat-seal layers 14 ofenvelope members 12 not less than their melting point at least when thevacuum is released. It is idealistic to heat envelope members 12 onlyduring the atmospheric introduction so as to reduce the heat load of theenvelope members.

The introduced atmosphere makes chamber 16 a have a higher pressure thanchamber 16 b. The difference in pressure between chamber 16 a andchamber 16 b brings envelope members 12 a into contact with envelopemembers 12 b, thereby being heat sealed along core member 13. Envelopemembers 12 a is larger in size than envelope members 12 b, and the outerperipheral edges of envelope members 12 a are held by chamber 16 withoutbeing heat sealed to envelope members 12 b. After the heat sealingbetween envelope members 12 a and 12 b, the outer peripheral edges,which have not been heat sealed, are cut off.

As described above, in vacuum heat insulating material 11, opposedheat-seal layers 14 are heat sealed along core member 13 by utilizingthe gas pressure such as atmospheric pressure due to the pressuredifference in chamber 16. Envelope members 12 are pressed uniformlythroughout the surfaces thereof so as to be heat sealed along coremember 13 without causing wrinkles or sealing defects. This extends theregion to be heat sealed so as to improve the sealing performance. As aresult, the vacuum heat insulating material having long-term reliabilitycan be provided.

The aforementioned processes are performed in a single chamber so as toimprove the production efficiency of the vacuum heat insulatingmaterial. In vacuum heat insulating material 11 according to the presentembodiment, the heat sealed portions where opposed heat-seal layers 14of the envelope members 12 are heat sealed to each other have a uniformthickness. This allows vacuum heat insulating material 11 to havehomogeneous sealing performance and also a smooth surface, which makes agood appearance.

In vacuum heat insulating material 11 of the present embodiment, coremember 13 is disposed between heat-seal layers 14 of envelope members 12having gas-barrier properties. Opposed heat-seal layers 14 are heatsealed to each other by heating entire envelope members 12 to thetemperature at which heat-seal layers 14 are melted and by applying theuniform pressure from outside to inside envelope members 12 throughoutfirst portion 51 of envelope members 12 that faces at least core member13 and second portions 52 of envelope members 12 that are in thevicinity of core member 13.

In vacuum heat insulating material 11 of the present embodiment, coremember 13 is sealed under reduced pressure between heat-seal layers 14of envelope members 12 having gas-barrier properties.

Opposed heat-seal layers 14 are heat sealed to each other by heatingentire envelope members 12 to the temperature at which heat-seal layers14 are melted and by applying the uniform pressure from outside toinside envelope members 12 to the entire envelope members 12.

In vacuum heat insulating material 11 of the present embodiment that hasthe aforementioned structure, opposed heat-seal layers 14 are heatsealed to each other by heating entire envelope members 12 to thetemperature at which heat-seal layers 14 are melted and by applying theuniform pressure from outside to inside envelope members 12 throughoutfirst portion 51 and second portions 52 of envelope members 12.Consequently, even when core member 13 has a comparatively largethickness exceeding 10 millimeters, the predetermined pressure can beapplied to the portions of envelope members 12 that do not have coremember 13 therebetween without compressing core member 13 too much. Theaforementioned portions mean where heat-seal layers 14 are to be heatsealed to each other. This ensures the heat sealing.

Consequently, even when core member 13 has a comparative largethickness, vacuum heat insulating material 11 is prevented fromsuffering wrinkles in the vicinity of core member 13, and the portionswhere envelope members 12 are in contact with each other can be securelyheat sealed by the atmospheric pressure. The region to be heat sealedcan be extended as far as the edges of core member 13 so as to improvesealing performance. The heat sealed portions where opposed heat-seallayers 14 are heat sealed to each other have homogeneous quality andreliability. As a result, vacuum heat insulating material 11 havinglong-term reliability can be provided.

In the present embodiment, the pressure applied for the heat sealing isa fluid pressure. Using a fluid facilitates the application of theuniform pressure to the entire envelope members 12. The pressure for theheat sealing in the present embodiment is directly applied by the fluid,without stressing or scratching envelope members 12. As a result, vacuumheat insulating material 11 with less occurrence of pinholes and othersimilar problems can be provided.

In the present embodiment, the fluid is a gas. A gas is easier to handleand has less adverse effects on envelope members 12 than a liquid, whichrequires after-treatment such as removal of the liquid from envelopemembers 12 when adhered thereto. The pressure applied by the gas in thepresent embodiment is atmospheric pressure. The atmospheric pressure canbe uniformly applied from outside to inside envelope members 12 to theentire envelope members 12 only by covering core member 13 with envelopemembers 12 in a space reduced in pressure substantially to vacuum andthen returning the reduced pressure space to normal pressure. Theatmospheric pressure is high enough for the heat-sealing, so that thereis no need to provide a pressure device. This simplifies the provisionof vacuum heat insulating material 11.

Heat-seal layers 14 are made of polyethylene. Since polyethylene can besealed at comparatively low temperatures, it becomes easier to performthe heat sealing by additional heating. As a result, vacuum heatinsulating material 11 can be provided at low cost. Furthermore,envelope members 12 each have protective layer 28 of polyethyleneterephthalate as the outermost layer. Providing envelope members 12 withthe outermost layers made of a material suitable for surface protectioncan make envelope members 12 more resistant to scratch and pierce andoccurrence of pinholes and other similar problems can be prevented. As aresult, vacuum heat insulating material 11 having long-term reliabilitycan be provided. Polyethylene terephthalate is inexpensive, so thatvacuum heat insulating material 11 can be provided at low cost.

In the case where the heat for the heat sealing is applied out ofcontact with envelope members 12, there is no need to use the hot platesor the like that fit the shape of core member 13. In addition, envelopemembers 12 have no stress due to creases or scratches and occurrence ofpinholes and other similar problems can be prevented. In the case wherethe heat for the heat sealing is applied by radiant heat from hot plates17, envelope members 12 can be heated out of contact with hot plates 17and also in a reduced pressure space. Although vacuum heat insulatingmaterial 11 of the present embodiment does not include absorbent, it caninclude it.

Second Embodiment

FIG. 4 shows a sectional view of a vacuum heat insulating materialaccording to a second embodiment of the present invention. FIG. 5 is aschematic sectional view of a production device for producing the vacuumheat insulating material. Vacuum heat insulating material 19 is made ofthe same materials as vacuum heat insulating material 11 of the firstembodiment. In FIG. 4, vacuum heat insulating material 19 has coremember 13 and two envelope members 12 which cover core member 13 andinside of envelope members 12 is kept vacuum. Envelope members 12 havefirst portion 51 which faces the core member; second portions 52 whichare in the vicinity of the core member; and third portions 53 which areoutside second portions 52. First portion 51, second portions 52, andthird portions 53 are unitary formed.

Envelope member 12 include heat-seal layer 14 a and heat-seal layer 14b, and heat-seal layer 14 a is heat sealed along core member 13.Heat-seal layers 14 a and 14 b of top and bottom envelope members 12 areintegrally heat sealed to each other. Heat-seal layers 14 a andheat-seal layers 14 b are different in thickness from each other, andheat-seal layers 14 b seal the peripheries of envelope members 12.Vacuum heat insulating material 19 is produced by using productiondevice 20 shown in FIG. 5. Production device 20 has top and bottom hotplates 17 and frame seal heaters 21 which heat seal the peripheries ofenvelope members 12 in chamber 16. Production device 20 is connected totop pipe 18 a and bottom pipe 18 b which are used to create or releasethe vacuum.

Envelope members 12 a and 12 b, and core member 13 are placed inproduction device 20. Chamber 16 is divided into two spaces 16 a and 16b by envelope members 12 a. Envelope members 12 are heated by top andbottom hot plates 17, and chamber 16 is evacuated through pipes 18 a and18 b. When chamber 16 reaches a predetermined degree of vacuum, frameseal heaters 21 seal the peripheries of envelope members 12 thatcorrespond to third portions 53. Pipe 18 a releases the vacuum only inchamber 16 a first, and then the vacuum in chamber 16 b is released soas to introduce the atmosphere. In this atmospheric introductionprocess, a pressure difference occurs between inside and outside vacuumheat insulating material 19, and envelope members 12 a and 12 b becomeinto contact with each other so as to be heat sealed along core member13. Such a control of atmospheric introduction improves sealing quality.

As described above, vacuum heat insulating material 19 has differentsurface conditions between the peripheries and the inner sides ofenvelope members 12. The peripheries correspond to third portions 53,and the inner sides correspond to first portion 51 and second portions52. The gas pressure is generated by the pressure difference betweeninside and outside vacuum heat insulating material 19, and the externalpressure is the atmospheric pressure. Therefore, there is no need toprovide a pressuring device, thereby vacuum heat insulating material 19can easily be provided.

In vacuum heat insulating material 19, envelope members 12 havegas-barrier properties and each include heat-seal layer 14 a andheat-seal layer 14 b, and core member 13 is disposed between heat-seallayers 14 a opposed to each other and heat-seal layers 14 b opposed toeach other. The entire envelope members 12 are heated to a temperatureat which heat-seal layers 14 a and 14 b are melted. Opposed heat-seallayers 14 b in the peripheries of envelope members 12 are heat sealed toeach other by frame seal heaters 21. Then, opposed heat-seal layers 14 aare heat sealed to each other by applying uniform pressure to the entireenvelope members 12 from outside to inside envelope members 12.

In vacuum heat insulating material 19 of the present embodiment,envelope members 12 have gas-barrier properties and include heat-seallayers 14 a and heat-seal layers 14 b, and core member 13 is sealedunder reduced pressure between heat-seal layers 14 a opposed to eachother and heat-seal layer 14 b opposed to each other. The entireenvelope members 12 are heated to the temperature at which heat-seallayers 14 a and 14 b are melted. Opposed heat-seal layers 14 b in theperipheries of envelope members 12 are heat sealed to each other byframe seal heaters 21. Then, opposed heat-seal layers 14 a are heatsealed to each other by applying the uniform pressure from outside toinside envelope members 12 to the entire envelope members 12.

In vacuum heat insulating material 19 of the present embodiment havingthe aforementioned structure, opposed heat-seal layers 14 b positionedat the peripheries of envelope members 12, that is, at third portions 53are heat sealed to each other by frame seal heaters 21. Then, opposedheat-seal layers 14 a are heat sealed to each other by applying theuniform pressure to entire envelope members 12 from outside to insideenvelope members 12 throughout first portion 51 and second portion 52 ofenvelope members 12. Consequently, even when core member 13 has acomparatively large thickness exceeding 10 millimeters, thepredetermined pressure can be applied to the portions of envelopemembers 12 that do not have core member 13 therebetween, withoutcompressing core member 13 too much. The aforementioned portionsindicate where heat-seal layers 14 a are to be heat sealed to each otherand heat-seal layers 14 b are to be heat sealed to each other. Thisensures the heat sealing.

Consequently, even when core member 13 has a comparatively largethickness, vacuum heat insulating material 19 is prevented fromsuffering wrinkles in the vicinity of core member 13, so that theportions of envelope members 12 that are in contact with each other canbe securely heat sealed by the atmospheric pressure. The heat sealedregion can be extended as far as the edges of core member 13 so as toimprove sealing performance. The heat sealed portions where opposedheat-seal layers 14 a are heat sealed to each other have homogeneousquality and reliability. As a result, vacuum heat insulating material 19having long-term reliability can be provided.

In the present embodiment, the pressure applied for the heat sealing ofheat-seal layers 14 a is a fluid pressure. Using a fluid facilitates theapplication of the uniform pressure to the entire envelope members 12.The pressure for the heat sealing of heat-seal layers 14 a is directlyapplied by the fluid, without stressing or scratching envelope members12. As a result, vacuum heat insulating material 19 with reducedoccurrences of pinholes and other similar problems can be provided.

In the present embodiment, the fluid is a gas. A gas is easier to handleand has less adverse effects on envelope members 12 than a liquid, whichrequires after-treatment such as removal of the liquid from envelopemembers 12 when adhered thereto. The pressure applied by the gas in thepresent embodiment is atmospheric pressure. The atmospheric pressure canbe uniformly applied from outside to inside envelope members 12 to theentire envelope members 12 by covering core member 13 with envelopemembers 12 in a space reduced in pressure substantially to vacuum andthen only by returning the reduced pressure space to normal pressure.The atmospheric pressure is high enough for the heat-sealing, so thatthere is no need to provide a pressuring device. This simplifies theprovision of vacuum heat insulating material 19.

Heat-seal layers 14 a and 14 b are made of polyethylene. Sincepolyethylene can be sealed at comparatively low temperature, it becomeseasier to perform the heat sealing by additional heating. As a result,vacuum heat insulating material 19 can be provided at low cost.Furthermore, envelope members 12 each have protective layer (not shown)of polyethylene terephthalate as the outermost layer. Providing envelopemembers 12 with the outermost layers made of a material suitable forsurface protection can improve scratch resistance and pierce resistanceso as to reduce pinholes and other similar problems. As a result, vacuumheat insulating material 19 having long-term reliability can beprovided. Polyethylene terephthalate is inexpensive, so that vacuum heatinsulating material 19 can be provided at low cost.

In the case where the heat for the heat sealing of heat-seal layers 14 ais applied out of contact with envelope members 12, there is no need touse the hot plates or the like that fit the shape of core member 13. Inaddition, envelope members 12 have no stress due to creases or scratchesand are reduced in occurrence of pinholes and other similar problems. Inthe case where the heating for the heat sealing of heat-seal layers 14 ais applied by radiant heat from hot plates 17, heat-seal layers 14 a canbe heated out of contact with hot plates 17 and also in a reducedpressure space. Although vacuum heat insulating material 19 of thepresent embodiment does not include an absorbent, it can include it.

Third Embodiment

FIG. 6 shows a sectional view of a vacuum heat insulating materialaccording to a third embodiment of the present invention. In FIG. 6,vacuum heat insulating material 22 has core member 24 and two envelopemembers 23 which cover core member 24 and inside of envelope members 23is kept vacuum. Envelope members 23 have first portion 55 which facesthe core member, second portions 56 which are in the vicinity of thecore member, and third portions 57 which are outside second portions 56.First portion 55, second portions 56, and third portions 57 are unitaryformed.

Vacuum heat insulating material 22 has peripheral fin 25 consisting ofsealing portion 26 and secured sealing portion 27. Envelope members 23are heat sealed to each other by the ordinary method in sealing portions26 and by additional heating in secured sealing portions 27. In otherwords, secured sealing portions 27 and sealing portions 26 correspond tosecond portions 56 and third portions 57, respectively, of envelopemember 23.

Envelope members 23 have the same structure as envelope members 12 ofvacuum heat insulating material 11 of the first embodiment shown in FIG.2. Envelope member 23 is made of a laminate film consisting of firstprotective layer 28, second protective layer 29, gas barrier layer 30,and heat-seal layer 14 in this order from outside to inside. Twolaminate films are opposite to each other. First protective layers 28are made of polyethylene terephthalate film, and second protectivelayers 29 are made of nylon film. Gas barrier layer 30 is made ofaluminum foil, and heat-seal layer 14 is made of very low densitypolyethylene (VLDPE) film, which is a kind of polyethylene. Thepolyethylene terephthalate film is 12 μm thick, the nylon film is 15 μmthick, the aluminum foil is 6 μm thick, and the very low densitypolyethylene (VLDPE) film is 50 μm thick.

A method of producing vacuum heat insulating material 22 is described asfollows with reference to FIG. 6.

Core member 24 is a glass wool board having a density of 275 kg/m3 anddried for one hour at 140° C. in a drying furnace. Envelope members 23are previously sealed at three sides to form a bag-shape. Then, coremember 24 is inserted into the bag-shape envelope member 23 under apressure reduced almost to a vacuum (10 pascals, for example). Theopening of envelope member 23 is pressed by hot plates so as to besealed, thereby forming sealing portions 26. Then, envelope member 23are taken out from the reduced pressure to obtain vacuum heat insulatingmaterial 22 that is the same as an ordinary vacuum heat insulatingmaterial. Peripheral fin 25, at this moment, have been pressed tocontact each other by the atmospheric pressure, and includes sealingportion 26 and secured sealing portions 27 that have not been sealedyet.

Next, in order to additionally heat vacuum heat insulating material 22,vacuum heat insulating material 22 is passed between top and bottomheaters so that the heat-seal layers in secured sealing portions 27 canreach their melting temperature. At this moment, envelope members 23 areheated by radiant heat from the heaters and the ambient temperature.Then, envelope members 23 is immediately cooled under the atmosphericpressure to produce vacuum heat insulating material 22, in which theentire envelope members including secured sealing portions 27 are heatsealed.

As described above, heat-seal sealing portions 26 of peripheral fins 25are heat sealed to each other first by heating the entire envelopemembers 23, and then secured sealing portions 27, that is different withsealing portions 26, are heat sealed to each other. This increases theseal width so as to improve sealing performance, prevents wrinkles orsealing defects, and improves gas-barrier properties. As a result, thevacuum heat insulating material having long-term reliability can beprovided.

The optimum temperature and duration of the additional heating can bearbitrary determined depending on the material and shape of the vacuumheat insulating material and the specification of the heaters. Sealingportions 26 are well heat sealed to each other by the atmosphericpressure. However, in order to protect the adhesion at sealing portions26, that is sealed beforehand, it is preferable that sealing portions 26are applied with an appropriate pressure.

In vacuum heat insulating material 22 of the present embodiment, coremember 24 is covered with envelope members 23 that include gas barrierlayer 30 and heat-seal layers 14. Inside of envelope members 23 arereduced in pressure and the peripheries of envelope members 23 are heatsealed to form sealing portions 26. The portions of envelope members 23inside sealing portions 26 where envelope members 23 are in contact witheach other are entirely heat sealed.

Consequently, the heat sealing can be performed as simply as the normalwell-known heat sealing process without causing wrinkles or sealingdefects. Furthermore, the heat-sealing is applied to secured sealingportions 27 where envelope members 23 used to be merely in contact witheach other and not sealed to each other. This extends the region to beheat sealed so as to improve sealing performance. As a result, vacuumheat insulating material 22 having long-term reliability can beobtained.

Furthermore, the heating device apply the uniform pressure to the heatsealed portions inside sealing portions 26, that is, secured sealingportions 27, and secured sealing portions 27 have no traces ofpressuring. As a result, envelope members 23 has no stress due tocreases or scratches, thereby vacuum heat insulating material 22 withreduced occurrence of pinholes and other similar problems can beprovided.

In the present embodiment, heat-seal layers 14 are made of polyethylene.Since polyethylene can be sealed at comparatively low temperature, itbecomes easier to perform the heat sealing by additional heating. As aresult, vacuum heat insulating material 22 can be provided at low cost.Furthermore, envelope member 23 have protective layer 28 of polyethyleneterephthalate as the outermost layer. Providing envelope member 23 withthe outermost layers made of a material suitable for surface protectioncan make envelope member 23 more resistant to scratch and pierce andreduces occurrence of pinholes and other similar problems. As a result,vacuum heat insulating material 22 having long-term reliability can beprovided. Polyethylene terephthalate is inexpensive, so that vacuum heatinsulating material 22 can be provided at low cost.

Vacuum heat insulating material 22 of the present embodiment is producedas follows: Core member 24 is covered with envelope members 23 includinggas barrier layers 30 and heat-seal layers 14. Inside of envelopemembers 23 are reduced in pressure, the peripheries of envelope members23 are heat sealed, and the non-sealed portions where envelope members23 are merely in contact with each other and not heat sealed to eachother are applied with heat sufficient to melt heat-seal layers 14. Thismethod allows to heat seal the non-sealed portions of envelope members23 that cannot be heat sealed by the ordinary method. In vacuum heatinsulating material 22 thus produced, the portions of heat-seal layers14 that are in contact with each other are entirely heat sealed to eachother.

In the method of producing vacuum heat insulating material 22 of thepresent embodiment, the heat may be applied out of contact with securedsealing portions 27. This allows envelope members 23 to be heatedwithout the hot plates or the like that fit the shape of core member 24.In addition, envelope members 23 have no stress due to creases orscratches and are reduced in occurrence of pinholes and other similarproblems.

Fourth Embodiment

FIG. 7 is a schematic sectional view of a production device forproducing a vacuum heat insulating material according to a fourthembodiment of the present invention. The method of producing a vacuumheat insulating material of the present embodiment is described asfollows with reference to FIG. 7. Vacuum heat insulating material 22 ismade of the same materials as vacuum heat insulating material 22 of thethird embodiment, and has the same structure as vacuum heat insulatingmaterial 19 shown in FIG. 5. In reduced pressure space 32, top andbottom of core member 24 are covered with envelope members 23, whoseperipheries are temporarily fixed to prevent misalignment between topand bottom envelope members 23. There are provided plane heaters 33above and below envelope members 23. While maintaining the reducedpressure condition, plane heaters 33 are heated to keep the surfaces ofenvelope members 23 at 140° C. to 170° C. for 10 to 30 seconds, therebymelting the heat-seal layers of envelope members 23. At this moment,envelope members 23 are heated by radiant heat from plane heaters 33.

Next, the entire peripheries are bonded to each other between pressureplates 34 so as to form sealing portions 26, and then the reducedpressure space is returned to a normal temperature and normal pressure.As a result, secured sealing portions 27 of vacuum heat insulatingmaterial 22 are pressed and sealed at the same time by the atmosphericpressure so as to heat seal the entire peripheral fins 25. Thus,peripheral fins 25 are entirely heat sealed, so that none of theportions of the envelope members that are in contact with each other isleft unsealed.

As described above, in vacuum heat insulating material 22 of the presentembodiment, secured sealing portions 27 are heat sealed immediatelyafter or almost at the same time as sealing portions 26 are heat sealedby heating the entire envelope members 23. This method prevents wrinklesor sealing defects so as to improve sealing performance and gas-barrierproperties. As a result, the vacuum heat insulating material havinglong-term reliability can be provided. Furthermore, these sealingportions are heat sealed almost at the same time in the same space, sothat it takes less time to produce vacuum heat insulating material 22.

Using the very low density polyethylene for heat-seal layers 14 canreduce the number of processes because it can be heat sealed at lowtemperatures. Using high-density polyethylene for heat-seal layers 14can have a wider applicable temperature range of vacuum heat insulatingmaterial 22, and can further improve the gas-barrier properties.

In the method of producing vacuum heat insulating material 22 of thepresent embodiment, core member 24 is covered with envelope members 23having gas barrier layers 30 and heat-seal layers 14 in reduced pressurespace 32. Heat-seal layers 31 are brought to a predetermined moltenstate while maintaining reduced pressure space 32 to a temperaturehigher than the melting point of heat-seal layers 14. Reduced pressurespace 32 is then returned to normal pressure, while pressing theperipheries of envelope members 23 so that envelope members 23 includingthe non-pressed portions can be heat sealed to each other. This methodallows envelope members 23 to be normally heat sealed by heat pressingand to be heat sealed by the atmospheric pressure at the same time, sothat it takes less time to produce the vacuum heat insulating material.

Fifth Embodiment

FIG. 8 is a schematic sectional view of a refrigerator main body as aheat insulating box according to a fifth embodiment of the presentinvention. In refrigerator main body 35, which is a heat insulating box,outer box 36 made of a steel plate and inner box 37 made of ABS resinform a space therebetween. The space is provided on one side thereofwith vacuum heat insulating material 22, and the remaining space isfilled with foam insulation material 38 made of rigid urethane foam.Refrigerator main body 35 includes refrigerating room 39, freezing room40, and machine room 42 having compressor 41 therein.

The refrigerator, that is the heat insulating box, of the presentembodiment maintains energy-saving performance for a long time by usingvacuum heat insulating material 22 with long-term reliability. Thelong-term reliability has been achieved by making vacuum heat insulatingmaterial 22 high in gas-barrier properties and resistant to scratch andpierce and reduced in occurrence of pinholes and other similar problems.The power consumption of the refrigerator is measured and it has turnedout to be about 20% lower than that of the refrigerators not havingvacuum heat insulating material 22. Using vacuum heat insulatingmaterial 11 of the first embodiment or vacuum heat insulating material19 of the second embodiment can provide the same advantages as usingvacuum heat insulating material 22.

As described above, in the vacuum heat insulating material of thepresent invention, the region to be heat sealed is extended as far asthe edges of the core member so as to improve sealing performance evenwhen a core member having a comparative large thickness is used. Theheat-seal layers are made of material suitable for heat sealing, and thesurface protective layer is made of a material suitable for surfaceprotection. This makes the vacuum heat insulating material higher inresistance to scratch and pierce and reduces an occurrence of pinholesand other similar problems. As a result, the vacuum heat insulatingmaterial has long-term reliability. Furthermore, a heat insulating boxsuch as an energy-saving refrigerator that uses the vacuum heatinsulating material can be provided.

Although the fluid used in the aforementioned first to fourthembodiments is atmospheric air, however, the fluid used in the presentinvention may be carbon dioxide, helium, or the like.

INDUSTRIAL APPLICABILITY

As described above, the vacuum heat insulating material of the presentinvention has been improved in gas-barrier properties, resistance toscratch and pierce, and reduction in occurrence of pinholes and othersimilar problems. These advantages allow the vacuum heat insulatingmaterial to have a deep groove, to be used in an environment subjectedto external impact, or to be used in a heat insulating box such as arefrigerator and other low temperature devices.

1. A vacuum heat insulating material comprising: a core member; andenvelope members having gas-barrier properties and including heat-seallayers, the envelope members being opposed to each other in such amanner that the core member is disposed between the heat-seal layers,wherein the envelope members are entirely heated to a temperature atwhich the heat-seal layers are melted, and the heat-seal layers are heatsealed to each other by applying uniform pressure from outside to insidethe envelope members to a first portion of the envelope members that atleast faces the core member, and to a second portion of the envelopemembers that is in a vicinity of the core member.
 2. The vacuum heatinsulating material of claim 1, wherein the core member is sealed underreduced pressure between the envelope members.
 3. The vacuum heatinsulating material of claim 1, wherein a third portion of the envelopemembers are previously heat-seated after an inside of the envelopemembers is reduced in pressure, the third portion being outside thesecond portion.
 4. The vacuum heat insulating material of claim 1,wherein the pressure is applied by a fluid.
 5. The vacuum heatinsulating material of claim 4, wherein the pressure is applied by thefluid directly to the envelope members.
 6. The vacuum heat insulatingmaterial of claim 4, wherein the fluid is a gas.
 7. The vacuum heatinsulating material of claim 6, wherein the pressure is atmosphericpressure.
 8. The vacuum heat insulating material of claim 1, wherein theheat-seal layers are made of polyethylene.
 9. The vacuum heat insulatingmaterial of claim 1, wherein each of the envelope members have aprotective layer made of polyethylene terephthalate as an outermostlayer thereof.
 10. A method of producing a vacuum heat insulatingmaterial, the method comprising: covering a core member with envelopemembers, each of the envelope members having a gas barrier layer and aheat-seal layer, evacuating an inside of the envelope members and heatsealing peripheries of the envelope members; and heat-sealing a portionby uniformly applying heat sufficient to melt the heat-seal layer to aportion where the envelope members are in contact with each other, theportion being inside the heat-sealed peripheries.
 11. The method ofproducing a vacuum heat insulating material of claim 10, wherein theheat is applied out of contact with the portion.
 12. The method ofproducing a vacuum heat insulating material of claim 10, wherein theheat is applied by radiant heat from a heater.
 13. A method of producinga vacuum heat insulating material, the method comprising: covering acore member with envelope members in a reduced pressure space, each ofthe envelope members having a gas barrier layer and a heat-seal layer;maintaining the reduced pressure space at a temperature higher than amelting point of the heat-seal layers so as to bring the heat-seallayers to a predetermined molten state; returning the reduced pressurespace to normal pressure, while pressing the peripheries of the envelopemembers; and heat-sealing the envelope members including a non-pressedportion of the envelope members by contacting the envelope members witheach other.
 14. A vacuum heat insulating material according to claim 1,said vacuum heat insulating material included in a heat insulating boxwhich further comprises: an outer box; an inner box; and a foaminsulation material filled in a space formed between the outer box andthe inner box; said vacuum heat insulating material provided between theouter box and the inner box, the vacuum heat insulating material beingat least partly buried in the foam insulation material.
 15. A method ofproducing a vacuum heat insulating material according to claim 1, saidvacuum heat insulating material included in a heat insulating box whichfurther comprises: an outer box; an inner box; and a foam insulationmaterial filled in a space formed by the outer box and the inner box; avacuum heat insulating material provided between the outer box and theinner box, the vacuum heat insulating material being at least partlyburied in the foam insulation material.